1. Field of the Invention
The present invention relates to a vehicle room lamp to be mounted to an inner lining of a vehicle roof and, more specifically, to a thermal insulation structure of a vehicle room lamp for preventing a case from becoming damaged by heat from a light bulb stored in the case of the room lamp.
2. Description of the Related Art
In manufacture of a vehicle room lamp, polypropylene which is low in cost has been employed as a case material for reducing the cost. When a light bulb with high heat value is used in such a case, there was a problem such that a terminal strip for mounting the light bulb to the case is heated by heat from the light bulb, or portion of the case where the terminal strip is to be mounted is thermally deformed (melted) by direct heat irradiation from the light bulb, whereby the terminal strip comes apart from the case.
Therefore, in order to solve such a problem, there is a technique disclosed in Japanese Unexamined Utility Model Registration Application Publication No. 4-5082. This technique is such that a terminal strip for a light bulb is mounted to a bulb cassette formed of expensive resin having high thermal resistant property, and the bulb cassette is detachably mounted to the case. In this structure, the terminal strip is prevented from coming apart by thermal deformation caused by the light bulb thereby becoming a state in which the lamp cannot be lit.
In the bulb cassette in the related art as described above, it is possible to prevent the mounting fixture from coming off the case due to thermal deformation. However, when a space in the case for accommodating the light bulb is small, there arises a problem such that a wall surface which defines the space is thermally deformed by heat from the light bulb, whereby the product value is lowered, and in the worst case, the entire case may become unusable due to thermal deformation of the wall surface.